It is known in the filtration arts to provide solid filtration media for gas or air filtration. Media used in the filtration of gases are typically in the form of pellets confined in a container forming a filtration bed through which the gas stream to be filtered is passed. Filtration of selected components in the gas stream may be accomplished by several different mechanisms such as by adsorption or absorption with the filtration media. Filtration may also be accomplished by a variety of other means such as a chemical reaction between the selected component(s) and the filtration media or even by physically trapping the component(s) within the filtration media.
The means to contact the gas stream with the filtration media typically involves placing the filtration media in a container to form a bed of filtration media through which a gas stream is passed. These containers typically have perforations or slots in a front and rear wall and four side walls and may have additional structural features forming a cassette holding the container which holds a defined depth of filtration media. The gas enters the front or rear wall, passes through the filtration media, and exits the other of the front or rear wall. The residence time of the gas in the filtration media is dependent upon the volumetric flow rate of the gas, the size and shape of the pellets forming the filtration media bed and void space therein, the depth of the bed as well as the configuration and orientation of the filter bed or cassette.
An example of a known filtration container is a flat box configuration having perforations in large planar walls spaced apart by four side walls. The spacing between the large planar walls may be as little as an inch, depending on desired residence time. The container is filled with filtration media by pouring into an opening in a side wall. The container is then typically placed within the cross-section of a duct or within a rack or frame through which the gas to be filtered is passed. A problem encountered with this configuration is that the pressure placed on the container is normal to the face of the container and causes bowing of the large planar walls which in turn subjects the filtration media to frictional forces releasing a portion thereof into the gas stream. Another problem encountered with this configuration is that the residence time of the gas within the filtration bed is relatively short since the flow of gas is normal to the filter.
Cassette configurations have been used to overcome some of the problems associated with the normal flow containers. One such design involves placing the filter container with a cassette at an angle with the direction of gas flow. This configuration reduces the bow of the container and provides for an increased residence time of the gas within the filter. Another design has been to place two containers in a “V” configuration within a cassette. However, many of these containers and cassettes have failed to provide the efficient and reliable filtration capability that is often times required.